There is a widespread misconception that once a ceramic tile floor is in place all water will be shed by the slope leading to the drain and will be removed via the drain. What is not understood is that, in fact, there is a substantial penetration of water through the grout into the mortar bed under the ceramic tile. The usage of the shower will determine how dry or wet the mortar bed will remain. Drains used with ceramic tile typically have small holes in communication with the mortar bed to release excess water. A liner must be placed under the mortar bed to prevent excess water from escaping and causing damage to the building.
In order to save time and expense attempts were made to place rigid polymer plastic bases preformed with sloped drainage under ceramic tile in lieu of building up and shaping a mortar bed. These preformed bases were found to have a number of disadvantages. There was no latitude for positioning the drain, the drain could only be positioned where an opening was left in the preformed polymer plastic base. There was a differential in expansion and contraction as between ceramic tile and the polymer plastic base. There was no adhesive cement able to accommodate or withstand the relative movement between the ceramic tile and the polymer plastic base resulting from the differential in expansion and contraction. The industry was forced to return to using shower liners whenever a ceramic tile floor was called for.
The shower liners that are presently in widespread use with ceramic tile consist of a one piece flexible membrane of polyvinylchloride approximately 30 millimetres in thickness. The flexible membrane is purchased in rolls approximately 4 feet wide and 50 feet long. It is rolled out to a desired length and cut to suit the dimensions of the mortar bed, allowing for a portion to be run up all walls adjacent the mortar bed to a height of approximately 6 inches. These shower liners have a number of inherent problems. Depending upon the dimensions of the mortar bed it may be necessary to over lap material and seal the same to form a water tight seam. The liner is fit in loose formation, tacked to studs along its peripheral top edge and folded at the corners. Bulges and wrinkles of excess material on walls and floor can create problems during installation. These bulges and wrinkles prevent ceramic tile backer board from fastening flush. It is difficult to compact cement over the bulges and wrinkles, these areas are weaknesses in the floor which are susceptible to cracks. After construction water can become trapped in the bulges and wrinkles leading to mildew problems. In a high percentage of cases leaks are discovered in the shower liner after installation. The only way the leaks can be discovered is through frequent usage. When the shower is used frequently the water level in the mortar bed is high. Accumulations of water escape into walls and ceilings if there is a leak which provides secondary drainage. In such a case, the building owner is fortunate if the leak is discovered before substantial water damage is sustained. The only mode of repair is total replacement of the ceramic tile, mortar bed and liner. A pin hole in the liner is virtually impossible to locate by visual inspection during installation. However, water leaking through such a pin hole can cause substantial damage. The reason damage to shower liners is so common is due to the large number of tradesmen who are involved in building construction working in and around the shower area. The construction of a bathroom in which the ceramic shower is to be installed involves drywallers, plumbers, electricians, and others. Other than the tile setter, few tradesmen are aware of the importance of the shower liner, and the consequences if it sustains a pin hole. Trades entering the shower area frequently damage the shower liner through carelessness. The carelessness can involve dropping a tool onto the liner, or dropping small sharp objects onto the shower liner and stepping on them. Nails and screws are dropped and stepped upon by framers and drywallers. Wires are snipped and stepped upon by electricians. All trades tend to place garbage and other objects in the shower area to get them out of the way when they are working.